The usage of carotenoid pigments such as astaxanthin is increasing in the field of food and feed additives as a colorant and/or as an anti-oxidant, in particular for aquacultered fish. Aquatic animals, like terrestrial animals, generally cannot synthesize astaxanthin or other carotenoids but several of these animals, including crustaceans, accumulate astaxanthin present in their diet. Crustaceans have the capability of converting carotenes to astaxanthin. Salmonid fish and red sea bream fish accumulate dietary astaxanthin but these fish cannot convert other carotenes to astaxanthin. Thus, the astaxanthin present in salmonid fish must be derived directly from dietary source.
Currently synthetic astaxanthin is employed as feed additive for coloration of farmed fish for providing its desired characteristic reddish colour. However, consumer concerns have resulted in an increased demand for providing natural astaxanthin to substitute the synthetically produced astaxanthin. This should also be seen in the light of the current general preference for natural products.
The expansion of the crustacean-processing industry has been accompanied by the production of large amounts of crustacean waste containing astaxanthin. Shrimp processing involves the removal of the head and hard carapace, which account for up to about 70% of the whole shrimps. Although pigmentation of fish flesh can be achieved by feeding the fish with crustacean waste, there are several disadvantages to this approach. These include the variable pigment level, the tendency of the raw crustacean waste to deteriorate rapidly, bulkiness and high transportation cost and a high chitin content. Thus, the content of carotenoid pigments in crustacean waste is too low compared to the undesirably high content of chitin and calcium for its use in large amounts in fish feed.
Various chemical methods for extracting pigments, e.g. from crustacean waste and their incorporation into fish feed have been described. Chen et al, Journal of Food Science, vol 47/3, 892–900, 1982 describes extraction of astaxanthin from crustaceans with soy oil alone or in combination with use of proteases. Use of organic solvents for extracting astaxanthin has also been described.
Several references disclose methods involving protease treatment for extraction of astaxanthin from crustaceans, cf. e.g.: Simpson and Haard, Journal of Applied Biochemistry, 7, 212–222, 1985; Chen and Meyers, Journal of Food Science, vol 47, 892–900, 1982. CA1,313,935 also discloses treatment of crustacean waste with protease. In Abstract of Papers, American Chemical Society, vol. 231 p7-IEC, 1997 is disclosed the extraction of carotenoproteins from crustacean wastes by means of trypsin.
JP 60-35057A describes extraction of orange dye from krill with a solvent and subsequently after the extraction adding lipase or an alkali to the extract solution to decompose fatty acid and using a fluid at supercritical state to separate the dye from the extract solution.
JP 62-00179A discloses the extraction and separation of colouring matter from krill, wherein protein is extraction with carbon dioxide in supercritical state from the krill using a protease.
JP 62-190090A discloses the extraction of pigment from vegetable material, such as carrot, pumpkin, by the use of enzymes, such as amylase, protease and cellulase.
In summary, there is a demand for substituting the synthetically produced astaxanthin presently on the market and one object of the present invention is to provide a method for providing natural coloured pigment, such as astaxanthin.